The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other forming a strong hollow column for support of the cranium and trunk. Various spinal disorders such as scoliosis, neuromuscular disease, and cerebral palsy may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders to straighten or adjust the spine into a proper curvature.
Generally the correct curvature is obtained through surgical procedures by manipulating the vertebrae into their proper position and securing that position with a rigid system of screws, rods, intervertebral spaces, and/or plates. During the surgical procedure, a tissue retractor may be inserted into a surgical incision to pull tissue away from the surgical site thus enlarging the viewing area for the surgeon. Tissue retractors form a surgical corridor including a proximal opening at the incision and a distal opening near the surgical site. Various instruments and implants may be inserted through the corridor. Exemplary tissue retractors may be found in U.S. Pat. No. 7,780,594 entitled “Retractor and Methods of Use” filed Oct. 6, 2006 and U.S. Application Publication Number 2008/0114208 entitled “retractor” filed Sep. 24, 2007.
The amount of tissue to be retracted depends upon the chosen approach as well as various patient characteristics. For example, in a lateral approach, more soft tissue may be present between the surgical incision and the surgical site near the vertebrae than in a posterior approach. Patient anatomical differences may also require various length retractors. The size, shape, and configuration of the retractor may be chosen based on these as well as other factors.
Typical tissue retractors include two or more elongated blades with proximal ends attached to a housing that is in turn attached to a surgical table. Each blade assembly may be attached to a separate portion of the housing and include various adjustment features for manipulating the blades to adjust and enlarge the viewing area. Often, the tissue retractor may hold the blades close together in a tubular configuration for concentric insertion over dilation tubes along a common longitudinal axis. The portions of the housing may translate or rotate relative to one another to gradually pull the blades apart from one another to expand the surgical wound.
When a retractor is opened to distract soft tissue the resistance load pressing on the distal end of the blades increases and causes conical deformation. As used herein “conical deformation” is when the distal end of the blades curve back towards the center of the portal opening forming a cone-like shaped tunnel where the distal opening at the exposed surgical site is smaller than the proximal portal opening. The conical deformation of the blades also causes a reaction force that pushes the retractor away from the surgical site. This requires that the surgeon take extra precaution to prevent the blades from lifting off the bone surface as the retractor is opened.
In order to compensate for blade conical deformation most retractors use a secondary adjustment mechanism. This mechanism typically provides an independent pivot action to cause the distal end of the blade to project further out radially with respect to the proximal end of the blade-a motion referenced herein as “toeing out” or “toe out.” The blade may toe out by turning a screw that acts on a lever or by using a biased torsional spring. To properly align the opened retractor the surgeon is required to make two independent adjustments for each blade requiring additional surgical time, and adds complexity and bulk to the jaws of the retractor. Due to the limited area available in the jaw area the adjustment mechanisms must be compact which limits the leverage available to counteract the torque generated by long length blades. This lack of adequate counter leverage leads to very large loads that are applied to small mechanisms. Failure and wear of the secondary blade mechanism is a common complaint for such retractors. Accordingly, there exists a need in the art to provide a soft tissue retractor that adequately compensates for the conical deformation of the blades during a procedure.
Furthermore, successful surgery is performed when using these retractors by preventing soft tissue from encroaching into the surgical site by slipping under the distal end of the blade. The prime factor in managing the dissection of soft tissue is maintaining contact of the distal end of the blades with the surface of the bone to prevent tissue encroachment. However, maintaining blade contact is difficult because the bone structure has a complex surface geometry that may cause the blade to lift as the blades are spread apart.
To reduce the risk of complications, current retractor systems rely on docking and stabilization of the retractor rigidly with at least one surgical table arm. It is often necessary for the surgeon to remove and replace a blade with a blade of a different length to accommodate the varying bone structure. This replacement is often required at the L4/L5 disc space where the retractor frame may have to be tilted to avoid contact with the iliac crest. Replacing a blade during a procedure adds time.
Adjustment mechanisms of the prior art have attempted to address the blade contact issue by the use of shims that project beyond the end of the blade and contact the bone surface. The shims are fit into a groove in the blade and slide down the entire length of the blade. This structure provides the disadvantage of requiring the use of a separate component that has to be mounted to an insertion instrument.
Another system to provide blade adjustment is the use of a telescoping blade that uses a nested blade that can be extended to the required length. However, this method of using nested blades increases the blade cross-sectional area causing a more bulky blade system that requires larger initial dilation and increased tissue expansion for an aperture during a procedure.
Accordingly, there exists a need in the art to provide a soft tissue retractor providing for depth adjustment to prevent encroachment of soft tissue during a procedure.